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Stock-Based Compensation - Performance Share Awards (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended 24 Months Ended
Dec. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]          
Allocated share-based compensation expense   $ 8.2 $ 11.0 $ 8.5  
Performance Shares Awards          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Award requisite service period   3 years      
Period for share issuance after vesting   60 days      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]          
Total compensation cost not yet recognized $ 4.4 $ 4.4 $ 3.4   $ 4.4
Total compensation cost not yet recognized, period for recognition   1 year 8 months 23 days 1 year 9 months 18 days    
Performance Shares Awards | Minimum          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Potential vesting percentage   0.00%      
Performance Shares Awards | Maximum          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Potential vesting percentage   200.00%      
Market Condition Performance Share Awards          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Expected dividend yield (percent)   0.00% 0.00%    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]          
Outstanding (in shares)   82,907      
Granted (in shares)   50,293      
Vested (in shares)   (29,293)      
Forfeited (in shares)   (7,748)      
Outstanding (in shares) 96,159 96,159 82,907   96,159
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]          
Outstanding, weighted-average grant date fair value (in dollars per share)   $ 53.92      
Granted, weighted-average grant date fair value (in dollars per share)   70.77      
Vested, weighted-average grant date fair value (in dollars per share)   56.84      
Forfeited, weighted-average grant date fair value (in dollars per share)   57.15      
Outstanding, weighted-average grant date fair value (in dollars per share) $ 61.58 $ 61.58 $ 53.92   $ 61.58
Performance Condition Performance Share Awards          
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]          
Outstanding (in shares)   41,454      
Granted (in shares)   24,861      
Vested (in shares)   (14,648)      
Forfeited (in shares)   (3,873)      
Outstanding (in shares) 47,794 47,794 41,454   47,794
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]          
Outstanding, weighted-average grant date fair value (in dollars per share)   $ 49.81      
Granted, weighted-average grant date fair value (in dollars per share)   60.11      
Vested, weighted-average grant date fair value (in dollars per share)   55.50      
Forfeited, weighted-average grant date fair value (in dollars per share)   52.10      
Outstanding, weighted-average grant date fair value (in dollars per share) $ 53.24 $ 53.24 $ 49.81   $ 53.24
Stock Appreciation Rights (SARs) [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Award requisite service period         4 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]          
Award performance period         2 years
Allocated share-based compensation expense $ (1.9) $ 0.7 $ 1.2